LTC4232 datasheet(10/20 Pages) LINER

10 / 20 page

LTC4234

4234fa

For more information www.linear.com/LTC4234

APPLICATIONS INFORMATION

The typical LTC4234 application is in a high availability

system that uses a positive voltage supply to distribute

power to individual cards. The complete application circuit

is shown in Figure 1. External component selection is

discussed in detail in the following sections.

Turn-On Sequence

Several conditions must be present before the internal

pass MOSFET can be turned on. First the supply VDD must

exceed its undervoltage lockout level. Next the internally

generated supply INTVCC must cross its 2.65V undervolt-

agethreshold.Thisgeneratesa25µspower-on-resetpulse

whichclearsthefaultregisterandinitializesinternallatches.

After the power-on-reset pulse, the UV and OV pins must

indicate that the input voltage is within the acceptable

Figure 1. 10A, 12V Card Resident Application

range. All of these conditions must be satisfied for a du-

ration of 48ms to ensure that any contact bounce during

the insertion has ended.

The MOSFET is turned on by charging up the GATE with a

charge pump generated 24µA current source whose value

is adjusted by shunting a portion of the pull-up current to

ground. The charging current is controlled by the INRUSH

circuit that maintains a constant slope of GATE voltage

versus time (Figure 2). The voltage at the GATE pin rises

with a slope of 0.35[V/ms] and the supply inrush current

is set at:

IINRUSH= CL • 0.35[V/ms]

This gate slope is designed to charge up a 1000µF capaci-

tor to 12V in 34ms, with an inrush current of 350mA. This

SLOPE = 0.35[V/ms]

GATE

OUT

VDD + 6.15V

VDD

4234 F02

Figure 2. Supply Turn-On

ADC

226k

1µF

20k

12V

4234 F01

0.1µF

*TVS Z1: DIODES INC. SMAJ17A

680µF

VOUT

12V

10A

VDD

Z1*

OUT

GND

IMON

RSET

20k

RMON

20k

ISET

CGATE

0.1µF

RGATE

100k

GATE

LTC4234

INTVCC

TIMER

SENSE–

SENSE

FLT

140k

20k

CCOMP

3.3nF

10k

UV = 9.88V

OV = 15.2V

PG = 10.5V

20k

150k

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